1. Field of the Invention
The present invention relates to a system for enhancing an assessment of the bottom electrode structure of a DC electric arc furnace, and more particularly, to a sensing device and sensor system for obtaining information representing the conditions of the bottom electrode structure of a DC electric arc furnace and which information may be used to operate the furnace.
2. Description of the Prior Art
A bottom electrode structure for a direct current (DC) electric arc furnace (EAF) has several thin electrode pins mounted in a refractory material with the lower ends of the electrode pins secured in a steel base plate and the refractory material supported by the plate. The base plate is provided with a connector for the connection of a power supply. The thin electrode pins are used so that their upper end portions may be less eroded by the molten metal pool formed in the furnace when the furnace is operated. Additionally, several electrode pins are used so that a sufficient electric current may be supplied through the electrode pins and into the molten metal pool or the liquid steel in the furnace. That is, when the furnace is operated, the electric current supplied by the power source, e.g. a DC power source, flows from the connector, through the base plate to the several electrode pins, and into the molten metal pool in the furnace through the electrode pins.
In a typical DC electric arc furnace, the power system supplies the power necessary to melt the charged scrap and raise the liquid steel to a tapping temperature. In general, two electrodes deliver the power to the furnace. An upper electrode which generally is graphite acts as a negative terminal, i.e. a cathode (−) and generates the high temperature electric arc within the furnace. The current passing through the electric arc makes its way through the charged scrap and eventually to the pool of liquid steel above the bottom electrode which acts as a positive terminal (+), i.e. an anode for the furnace's DC power system and which bottom electrode is in direct contact with the liquid steel. The bottom electrode is part of the bottom structure for the EAF and includes the plurality of thin electrode anode pins discussed in the preceding paragraph.
It is common practice to assess the conditions of the bottom electrode by measuring the temperature of several electrode pins to determine the conditions of the refractory material in the bottom structure of the EAF and of the interface between the liquid steel and the bottom electrode. These conditions generally cannot be observed during operation of the EAF and can only be estimated from measured temperature profiles and trends.
This common practice of assessing the conditions of the bottom of an EAF involves a single point temperature measurement of the bottom electrode, that is, only one temperature measurement is made along each of the anode electrode pins from a select group of anode electrode pins. For this temperature measurement, the present practice is to select a distributed sub-set of anode electrode pins and to monitor a temperature point in each of these anode electrode pins of this sub-set. The monitored pins have a longitudinal center bore starting at the distal end at the base plate connection and extending upwardly to a desired depth within the surrounding refractory material. A temperature sensor of matching immersion depth is inserted into the longitudinal center bore of each of the anode electrode pins of the distributed sub-set of anode electrode pins so that the temperature measuring point of each of these anode electrode pins is at the top of the bore between the base plate and the liquid steel. The sensor wiring from this group of monitored electrode pins is routed from the furnace to a PLC remote I/O cabinet where the analog temperatures are detected by a control and monitoring system. Through this arrangement, the temperature magnitude of each anode pin of the sub-set is continuously monitored, trended and displayed in graphical form for visual observation by the operator of the furnace. Presently, this is the only data available for evaluating the conditions of the bottom electrode structure in an EAF. The integrity and longevity of the bottom electrode structure is directly related to the productivity of the EAF.
There is therefore a need to provide additional data for evaluating or assessing the conditions of the bottom electrode structure and to control the electrical power input of the EAF in order to manage the optimization of the bottom electrode.